1. Field of the Invention
The invention is concerned with the manufacture of metal strip material.
2. Description of the Prior Art
Articles such as springs, diaphragms, bellows, clips, electrical contacts, and small structural parts are typically manufactured by stamping from rolled strip material made from a cast ingot. Among desirable mechanical properties of such material are high yield strength and high ductility; other desirable properties are corrosion resistance, high electrical conductivity, and ease of soldering.
Among alloys suitable for applications such as those mentioned above are phosphor-bronze and beryllium-copper alloys as discussed, respectively, in G. R. Gohn et al, "The Mechanical Properties of Wrought Phosphor Bronze Alloys", American Society for Testing Materials, 1956 and G. R. Gohn et al, "The Mechanical Properties of Copper-Beryllium Alloy Strip", American Society for Testing and Materials, 1964. Up until recently, copper-nickel-tin alloys were not considered to be viable substitutes for phosphor bronze or copper-beryllium alloys due largely to inadequate formability of available copper-nickel-tin alloys. Investigations into the properties of such copper-nickel-tin alloys are described, e.g., in E. M. Wise et al, "Strength and Aging Characteristics of the Nickel Bronzes", Metal Technology, No. 523, January 1964, pages 218-244; E. Fetz, "Uber Aushartbare Bronzen Auf Kupfer-Nickel-Zinn-Basis", Zeitschrift fur Metallkunde 28, 1936, pages 350-353; and A. M. Patton, "The Effect of Section Thickness on the Mechanical Properties of a Cast Age-Hardenable Copper-Nickel-Tin Alloy", The British Foundryman, April 1962, pages 129-135, and exemplary metallurgical processing of such alloys is disclosed in U.S. Pat. No. 1,816,509, "Method of Treatment of Nonferrous Alloys", E. M. Wise, July 28, 1931.
In contrast to the relatively brittle copper-nickel-tin alloys dealt with in the above-mentioned references, U.S. Pat. No. 3,937,638, "Method for Treating Copper-Nickel-Tin Alloy Compositions and Products Produced Therefrom", issued to J. T. Plewes on Feb. 10, 1976, and assigned to the assignee hereof, discloses alloys which are strong as well as ductile. Such combination of properties is achieved by thermomechanical processing involving cold working by an amount of at least 75% area reduction followed by aging at a temperature depending on alloy composition and amount of cold work. The composition of these alloys is characterized in that such alloys are in a single phase state at a temperature near the melting point of the alloy but in a two-phase state at room temperature. It is believed that the unusual combination of high strength and high ductility achieved is due to inhibition of second phase precipitation at the grain boundaries in favor of a so-called spinodal transformation, which characteristically leads to fine dispersement of the second phase throughout the first phase. More recently, it has been discovered that certain quaternary alloys also undergo such a spinodal transformation. These alloys are disclosed in copending application J. T. Plewes 4, Ser. No. 685,263, filed May 11, 1976, now U.S. Pat. No. 4,052,204, and are obtained by substituting substantial amounts of a fourth element for a corresponding amount of copper in the ternary alloys disclosed in U. S. Pat. No. 3,937,638.
Due to their high strength, high ductility, and low cost spinodal copper-nickel-tin alloys are of interest as potential substitutes for phosphor-bronze and copper-beryllium alloys in the manufacture of strip material. While the alloys disclosed in U.S. Pat. No. 3,937,638 and copending application, J. T. Plewes 4, Ser. No. 685,263, are suitable for the manufacture of strip material, use of the resulting strip is most advantageous in applications which do not require sharp bending of the rolled strip such as would cause creasing of the strip in a direction having a substantial component parallel to the rolling direction. Due to anisotropy, i.e., directionally nonuniform formability, attempts at imparting such creases to a rolled strip may result in breakage of the strip.